Switch to MaterialComponents theme

Summary:
Androidx introduced new Materialcomponents themes, use them instead of
Theme.AppCompat. This also causes AlertDialogs and PreferenceDialogFragments
to be styled correctly

Before	After

(Ok button is disabled if you are wondering)

Test Plan: Apply patch, verify everything still looks as expected

Reviewers: KDE Connect, albertvaka

Reviewed By: KDE Connect, albertvaka

Subscribers: kdeconnect

Tags: KDE Connect

Differential Revision: https://phabricator.kde.org/D18039